Almost the same problem here: my fan only runs on high. I've read over at
The Contour Enthusiasts Group : CEG that it is because the fan relay has gone bad. Easy replacement it seems:
How to: Blower Motor Resistor Replacement (Fan only works on high!) - CEG Forums
I'm going to try this solution first, then will continue following your thread here with interest for an alternate possible solution.
Great post! Hopefully we can find a solution together.